But people don't say that a lot in Mexico, at least not where I'm from, anyways in my area a lot of people used "Que onda" for what's up "Hasta Luego" for see you later =] and a lot of other stuff =] hehe

I got a few :) SCREAM! AIM! FIRE! SAY HELLO TO MY LITTLE FRIEND! SHPOOPLE!!! or the prayer from the boondock saints: "And Shepherds we shall be For thee, my Lord, for thee. Power hath descended forth from Thy hand Our feet may swiftly carry out Thy commands. So we shall flow a river forth to Thee And teeming with souls shall it ever be. In Nomeni Patri Et Fili Spiritus Sancti."

I wouldn't paste a permanent message on the cannon, I'd have an erasable whiteboard or a chalkboard with a piece of chalk or a marker tied to it. This way, if I wanted to blow someone up with it, I could write their name on it; IE:

This one's got your name on it ;)

And then I'd erase it after finishing the task and write the next name on the board.

I suggest "For those about to Rock we Salute you!". You probably know this but it is a famous song by AC/DC where they wheel out these huge cannons on stage and fire them like crazy at the end of their concerts! I had a larger cannon until I put just a little too much powder in it....oops. Now that is a story.....

Eat My (and then whatever the cannon shoots for example potatoes) or Suck My Cannon!!! or Suckazz!!! or Ive Got Huge Guns!!! or This is the smallest of my guns!!! or Kazzam!! (as you can see i hav a lot of ideas)